Induction furnace



Jan. 14, 1930. P. E. BUNET INDUCTION FURNACE Filed May 25, 1928 2 Sheets-Sheet 1 .c Wm kw M w .MW m m I w W P canoe. F 0 660 Ill/561471 mg W aooooo o Patented Jan. 14, 1930 UNITED STATES PATENT OFFICE PAUL EMMANUEL BUNET, OF VERSAILLES, FRANCE, ASSIGNOR OF ONE-HALF'TO SOCIETE ACIERIES DE GrENNEVILLIERS, OF GENNEVILLIERS, SEINE, FRANCE, A

CORPORATION OF FRANCE INDUCTION FURNACE Application filed May 25, 1928, Serial No. 280,585, and in France June 2, 1927.

Certain induction furnaces, in the present state of their construction, are composed of a single primary circuit in the form of a solenoid surrounding the material to be heated, placed in a suitable crucible. The magnetic circuit is closed entirely in the air. The frequency employed varies in periodicity from some tens per second to several tens of thousands. The disadvantages of this arrangement are numerous.

The magnetic flux is closed in the air, but it traverses adjacent bodies, preferably magnetic bodies, which results in lowering the efiiciency and the power factor. I It is almost impossible to protect or armour the furnaces, and it is diflicult to render them oscillating, tilting, or in general movable, because that implies a mechanical equipment which would be traversed by the lines of magnetic force.

The present invention remedies these disadvantages; it consists in disposing a few magnetic iron cores externally of the primary circuit of the furnace in such a way as to guide or direct the flux and to reduce the reluctance of the magnetic circuit substantially to that of the air in the part to be heated. WVhilst it would be inconvenient to have magnetic iron cores in the, centre of the furnace,which is reserved for a crucible of simple form, their presence external ofthe prlmary solenoid presents no disadvantage.

The accompanying drawing represents by way of example different forms of carrying out the invention- Figure 1 is a sectional elevation of the induction furnace.

Figure 2 is a horizontal section along the line 22 of Figure 1.

Figure 3 is a view partly in section and partly in elevation illustrating a modification of the invention.

Figure 4 is a similar view illustrating a modification of the embodiment shown in Figure 3;

Figure 5 is a view partly in elevation and partly in section illustrating a modification of the invention embodying several systems of circuits.

Figure 6 is a fragmentary view partly in section and partly in elevation illustrating a further modification.

Figure 7 is a similar view illustrating the embodiment shown in Figure 6.

Figure 8 is a view partly in elevation and partly in vertical section illustrating an inductor circuit embodying one or more oblique turns fed at low tension.

Figure 9 is a View partly in elevation and partly in section illustrating a further modification of the invention.

Figure 10 is a vertical section of a furnace fed by a split primary winding.

Figure 11 is a horizontal section of a furnace subjected to an alternating flux.

Figure 12 is a diagrammatic horizontal Eection of a modification with a rotating Figure 13 is a vertical section of another modification with rotating flux.

Figure 14: is a vertical section of a furnacewith localized heating.

In the form of construction shown in Figures 1 and 2, there are arranged external of the primary winding E one or more systems of laminated magnetic cores F. It will be seen that-the reluctance of the magnetic circuit will be reduced to that of the air over the height of the crucible or a very slightly greater height, the reluctance of the iron being readily made negligible even for fairly high frequencies by maintaining in the majority .of cases the thicknesses of the laminations normal in current practice. This allows in particular the construction of furnaces of large diameter and small height, if desired, instead of being limited as has been the case hitherto to a form of construction resembling that which is understood currently as a long solenoid.

The lower branch F of the magnetic circuit may moreover be suppressed wholly or in part. Likewise the magnetic circuit can be extended at the upper end by portions such as F which can be stopped at F in order not to interfere with the inspection of the crucible; the parts F may also be rendered wholly or in part integral with the cover F The armouring A and the external bodies are thus protected from any disadvantageous induction;

A furnace of this kind is thus rendered strong, and it is seen at once that it can be transported or made to oscillate or tilt, as may be desired.

This arrangement may be combined with that which the applicant has described in his application for patent filed on the same day for improvements in magnetic-core induction furnaces, Serial No. 280,584. Figure 3 of the accompanying drawing represents a combination of this kind. In this case the inductor circuit is constituted by one or more big coils C surrounding the crucible B to be heated, and is fed at very low tension by one or more supplementary turns D arranged around the primary winding E. The magnetic circuit F may be completed as shown in Figure 4; in such a way as to embrace the windings D and E.

With such an arrangement orsimilar arrangements, there may be provided, instead of a sin le system of circuits C D, several systems 1 C C D l) D (Figure 5) and in particular the circuits C G C can be spread or distributed over the height of the crucible. By varying the proportion of the total current in each of these systems C C C D D D, and employing therefor any known electrical arrangements, the proportion of the currents induced in any given portion of the height of the crucible can likewise be varied.

It is evident moreover that the" crucible to be heated may be placed perpendicularly to the air gap, the inductor circuit E being quite close to the crucible B, as shown in Figures 6 and 7. Since the coils of the winding E would be an obstruction to the displacement of the crucible, the magnetic circuitcan be disposed in such a way as to allow of opening it for the removal or the replacement of the crucible' For example it may be made to pivot around an axis G as shown in Figure 6.

The inductor circuit C may likewise be constituted by one or more big turns fed at very low tension, the primary being at E (Figure 8).. 4

There may'likewise be carried out an arrangement analogous to that ofz-Figure 3, with a crucible B which is rectangular for example (Figure9), and an articulation at G of a portion of the magnetic circuit in order to allow theidisplacement of the crucible.

The partial addition of iron in the magnetic circuit allows of utilizing polyphase feed, contrary to what is the case in the present forms of furnaces with insufficiently directed magnetic circuit. In Figure 10, the primary circuit is split into three sections E E E while the magnetic cores produce three magnetic circuits I L U. Instead of three sections any number might be adopted. With the arrangement of Figure 10, the feed can be of three phase, but what is most advantageous for the purpose to be served, the feed can in general be of three or any other number of separate circuits of the same phase or not and adjustable at will. It is thus possible to concentrateflthe heat more particularly in any desired portion of the crucible, at any selected moment of the operations, which is sometimes very important.

In the arrangement represented in Figure 11 the flux traversing the crucible B is an alternating flux. The feed can be fed with polyphase current, three-phase for example, and induction applied to the crucible by means of 'a rotating flux, according to Figure 12, where H is the stator of an asynchronous motor or of an alternator with internal slots and winding (not shown in the drawing) and B the crucible of the induction furnace.

In the form of construction of Figure 13, which shows a vertical section taken upon the axis of the stator H, the crucible is constituted by a thin annulus or coil B in the middle ofwhich is arranged an iron core K. This coil is the seat of currents induced by the rotating flux issuing from the stator H. There can thus be obtained a balanced threephase furnace. The metal fused in B assumes a movement of rotation under the influence of this flux. By means of dissymmetries in the cross section of the crucible B, there can be produced a circulation between an upper reservoir L and the crucible B.

The constitution of continuous furnaces is also of great importance. Figure 14 represents a continuous furnace in the shape, for

example, of a long vertical cylinder B. Heating is required to take place in the region M N; at 0 there is indicated the material next to be treated, introduced at '0 at P is the material after having reacted, which is withdrawn through the tra P either continuously or at intervals. everal materials can be caused to pass through, inparticular solids and gases, travelling in the samedi'rection or in opposite directions, with recuperation of heat in the well known manner.

It may be desired toheat the portion M N by induction by rneans of a helix E traversed' by a high frequency current, the material being conductive or only the wall of the furnace.

The subject of the present invention allows an easier construction of this type of furnace, since the magnetic flux can be directed towards the member M N only, by using cores F; if desired, there may be arranged several heating zones at various distances apart or contiguous as in Figure 10; at the same time there can be provided an armouring of metal plates A.

This will be particularly advantageous in the case of rotary furnaces having a greater or less inclination to the horizontal, instead of being vertical as in Figure 14. The material then passes of itself from the upper extremity O to the extremity P Benefit may be derived from the advantages obtained by the addition of magnetic cores as regards the direction of the flux and the reduction of the reluctance, in order to modify,to the greater facility of the reactions to be elfected, the diameter of the heating region or regions A B, either making them larger or smaller than V of thefurnace.

What I claim is:

1. An induction furnace, comprising a working zone, an inductor winding disposed around said zone for heating said zone, and

a small number of magnetic cores arranged externally of said inductor winding and adapted to direct the flux upon said working zone. Y

2. An induction furnace, comprising a working zone, an inductor winding, consisting of several sections disposed around said zone for heating respective sections of the working zone, and a small number of magnetic cores arranged externally of said inductor winding and adapted to direct the flux upon the several sections of the working zone.

3. An induction furnace, comprising a working zone, a low voltage inductor wind-' ing disposed around said working zone for heating said zone, a smallnumber of magnetic cores arranged externally to said inductor winding, and a primary winding, arranged around said magnetic cores and adapted to effect a previous tranformation to the low voltage of the inductor.

In testimony whereof I have signed my name to this specification.

PAUL EMMANUEL BUNET.

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